I don't know if you are still active with this thread but thought you may be able to give me some advice. My husband and I are transforming our 24 ft. diameter above ground decked in swimming pool into a fish pond so we can be a bit more independent food-wise. My husband likes feeding the fish; they know what's happening when he shows up and come to twirl in front of him for their food and are confident enough to make big splashes. When it's beastly hot or raining or cold they stay in the depths.
The pool/pond is very green and murky. The algae problem needs to be addressed. I want to make a bio-filter of two 55 gallon food grade plastic barrels we bought from the local co-op and a bog filter using a 5 foot diameter, 1 foot deep kiddy pool. If my calculations are correct we have between 50,000 to 55,000 gallons of water that needs filtering. The water level is normally about 4 feet deep but we have the egress blocked so when it rains a lot there can be 5 feet of water in it or more. I have a submersible pump covered with a poly-fil batting wrap filter over a milk crate that moves that much water every eight hours; right now we are using it as a fountain to increase O2. I can't find the information as to how big a bio-filter would be needed for that much water. The calculations I saw were beyond me. Also I have several strengths of Hydrogen peroxide to help with the algae overgrowth and instructions to dilute it down to 3% for fish safety.
I can use rainwater runoff from the garage to fill the pool/pond when it's dry too long which probably needs a pre-filter for any roof or other debris. Our county buys its water so I am not using that to top up the water level. It has rained sufficiently to refill it so far. We have one small mouth bass, many Bluegills, and several fat catfish. Paul has "fed" the bass 5 pounds of minnows occasionally. We plan to eat the bass and bluegills this fall though we could leave them overwinter - they did fine last winter even with an occasional layer of ice. We have a bit of an ecosystem with the frogs laying their eggs and the flying insects laying their eggs on the surface of the water and other critters that visit. Some frogs manage to escape the fish who really like the frog eggs and tadpoles. Paul tried to rescue a frog he thought was stuck in the pool but it came back. I have rescued snakes but rarely. Years ago a squirrel must have fallen through the ice and drowned, found in the spring. A heron stopped by to check us out but I think the pool depth discouraged it from fishing and now the birds would be confronted with the sail shades. My compost buckets produce maggots we can feed the fish and I've made a simple non-smelly maggot farm which is strung over the water. When the maggots try to go down through the holes in the bottom as they would into the ground they find fish waiting. I've made structures from plastic lattice for shade and so smaller fish can hide in them giving them some chance of avoiding the bigger fishes hunting. The sail shades positioned over the water provide some relief from the blasting sun and tall trees also shade the pool in the late afternoon. The lattice structures float loose providing some shade. Initially, the only shade had been under the Rubbermaid steps.
I saw an article about using window screen instead of the poly-fil over the crate the pump is housed in. That sounds much easier to clean and nicer than trying to clean the algae soaked poly-fil. I was using the barrels for water for the garden but think this is less problematic and way more effective and necessary for the pool/pond. My husband advised that the barrel rim was necessary for strength and to prevent cracking. He pulled out the reciprocal saw for me and I managed to make the starter hole and used the saw to open the tops of the barrels. They already have holes I made for the rainwater collection kit from Walmart (available online as well) which holes I think I can use for the proposed filtration system with some modifications. I like the plans which call for the water coming in the top down to the bottom and filtering up to the overflow. That only requires one pump push up. I plan to use hose to move water from the pump to the barrels; the pump came with attachments for various uses. I will need more lava rock, a grate to keep it off the bottom, pebbles and scrubby filter discs for the large barrels and pebbles, pvc and plants for the bog garden. The pool deck is somewhat old as well and so we plan to reinforce it with outdoor rated 3/4 inch plywood under the bog garden.
Thanks for letting me share our plans and concerns.
